A computer chassis has many functions. First, it serves as a shelter to contain electronic and mechanical components of a computer, protecting them from harmful contact with external mechanical or electrical forces. Second, it serves as a mounting structure to which the components are secured in a prescribed relative position to allow convenient interconnecting of the components.
Finally, the chassis serves as a barrier for electromagnetic interference ("EMI") caused by electromagnetic fields generated within or without the chassis. As computers have grown more powerful, the electronic components thereof have become faster, increasing the potential for generation of interfering (and often illegal) radio frequency interference ("RFI"). Further, the electronic components have themselves become more sensitive to RFI generated externally. Therefore, good chassis design dictates that there not be open ports in the chassis that can emanate or admit EMI. Further, the chassis should provide a grounding path for the energy contained in the EMI.
With these functions in mind, the manufacturing process for electronics chasses for computers, and for personal computers ("PCs") in particular, is at least a three-step process depending, in large part, on the final desired shape of the chassis, the manner in which the chassis is to be secured to its environment and the manner in which electronic components are to be secured within the chassis.
Manufacture of a typical chassis (generally a box-like structure) begins by stamping parts of the chassis out of sheet metal with a die press. The stamping step yields one or more flat sheets of metal having a desired geometry. The flat sheets are then bent or folded to form portions of the finished chassis. In the bending step, various edges of the flat sheet are brought into proximity with one another to form edges and corners of the chassis portions. The edges or corners may be spot welded, soldered or brazed together to create a permanent bond. Finally, screws or other removable fasteners may be used removably to join the chassis portions together to form a rigid, mechanically sturdy chassis, to form a barrier as against EMI emanating from the components in the chassis, to shield the components from stray EMI from without the chassis and to form good electrical conductivity in the chassis for grounding purposes, as described previously.
During the stamping step, one or more ports may be formed in the chassis portions by completely shearing portions of the metal away with the die press. The ports are provided for the purpose of accepting electrical connectors therethrough. The electrical connectors allow interconnection of the components within the chassis to equipment outside the chassis. However, given the open architecture of IBM-compatible PCs and the myriad of possible hardware and connector configurations, it is difficult task to provide a chassis capable of accommodating all of the possible configurations.
Again, it is unacceptable to provide a universal chassis having ports for every conceivable hardware option, as unoccupied open ports on the chassis rear wall compromise EMI shielding (and ultimately run afoul of mandatory Federal Communications Commission RFI emission certification).
Therefore, to accommodate some degree of universality, prior art chassis portions often include partially-sheared portions (so-called "punchouts") that cover ports. Because they are only partially-sheared, punchouts are electrically coupled to the remainder of the chassis rear wall substantially entirely around their perimeter and thus provide an EMI shield. If it is desired to mount a connector through a particular port, the punchout is removed with a prying or punching tool, thereby exposing a port. If it is desired to leave the port empty, the punchout remains in place, thereby retaining EMI shielding. In this way, a single, universal chassis may be configured to contain a variety of differing hardware and connector options.
Unfortunately, with electronic components and their chasses shrinking in size and an ever-growing number of options in computer hardware configuration, limitations in rear chassis wall area have become acute. It is becoming increasingly difficult to provide a sufficient number of punchout-covered ports.
The limitation in rear wall area is particularly frustrating when hardware configurations are mutually exclusive. For instance, in PCs, there are two different small computer systems interface ("SCSI") standards: SCSI III (using a wider, 68 pin electrical connector and thus called "SCSI Wide") and SCSI II, using a narrower, 50 pin electrical connector and thus called "SCSI Narrow"). Often, a single PC does not need to contain connectors for both SCSI III and SCSI II. However, because the connectors for SCSI III and SCSI II are of different predetermined dimensions, two separate ports (covered by punchouts) must be provided on the rear wall of every PC chassis, only one of which is ultimately exposed depending upon the SCSI standard adopted in each PC. Thus, more rear wall area is required than should be.
Accordingly, what is needed in the art is a way of making each chassis port selectably configurable in size, such that a single configurable port can adapt to different alternative electrical connectors, thereby conserving rear wall area.